The invention relates to a process for reducing the agglomeration tendency of the hydrates of natural gas, petroleum gas or other gases, by the use of at least one additive. The gases which form hydrates can in particular incorporate at least one hydrocarbon chosen from among methane, ethane, ethylene, propane, propene, n-butane and isobutane and optionally H.sub.2 S and/or CO.sub.2.
These hydrates form when water exists in the presence of gas, either in the free state, or in the state dissolved in a liquid phase, such as a liquid hydrocarbon, and when the temperature reached by the mixture of in particular water, gases and optionally liquid hydrocarbons, such as oil, drops below the thermodynamic hydrate formation temperature, which is given for a known gas composition and when the gas pressure is fixed.
Hydrate formation is feared, particularly in the petroleum and gas industries, where the hydrate formation conditions can occur. Thus, in order to reduce the costs of the production of crude oil and gas, both from the investment standpoint and from the standpoint of exploitation, one procedure envisaged, particularly in the case of ocean production, is to reduce or eliminate the treatments applied to the crude or gas to be transported from the field to the coast and in particular all or part of the water is left in the fluid to be transported. These ocean treatments generally take place on a platform on the surface close to the field in such a way that the initially hot effluent can be treated prior to the thermodynamic hydrate formation conditions being reached as a result of the cooling of the effluent with the sea water.
However, as occurs in practice, when the requisite thermodynamic conditions for the formation of hydrates occur, the agglomeration of the hydrates leads to the filling and blocking of the transportation pipes as a result of the formation of plugs, which prevent any passage of crude or gas.
The formation of hydrate plugs can stop production and therefore cause significant financial losses. Moreover, the restoration to service of the installation, particularly in the case of ocean production or transportation may be far from easy, because it is very difficult to decompose the hydrates formed. Thus, when the production of an underwater deposit of natural gas or petroleum and gas containing water reaches the surface and is then transported to the bottom of the ocean, as a result of the lowering of the temperature of the effluent produced, the thermodynamic conditions are obtained for the formation and agglomeration of hydrates, so as to block the transfer pipes. The temperature at the bottom of the ocean can e.g. be 3.degree. or 4.degree. C.
Conditions favorable for hydrate formation can also occur in the same way on land, in the case of pipes which are not buried or not adequately buried in the ground, e.g. when the ambient air temperature is low.
To avoid these disadvantages, the prior art has sought to use products which, added to the fluid, could act as inhibitors by lowering the thermodynamic hydrate formation temperature. These are in particular alcohols such as methanol, or glycols, such as mono, di or tri-ethylene glycol. This solution is very onerous, because the quantity of inhibitors to be added can reach 10 to 30% of the water content and these inhibitors are difficult to recover in a complete manner.
There has also been a recommendation to isolate the transfer pipes, so as to prevent the temperature of the transported fluid from reaching the hydrate formation temperature under the operating conditions. However, such a procedure is very expensive.
In addition, several nonionic or anionic surfactants have been tested for their effect of delaying the formation of hydrates within a fluid containing a gas, particularly a hydrocarbon and water. Reference can e.g. be made in this connection to the article by Kuliev et al: "Surfactants studied as hydrate - formation inhibitors" Gazovoe Delo, No. 10, 1972, pp. 17-19, reported in Chemical Abstracts 80, 1974, 98122.
A description has also been given of additives able to modify the hydrate formation mechanism, because instead of rapidly agglomerating with one another and forming very solid plugs, the hydrates formed disperse in the fluid without agglomerating and without obstructing the pipes, when the temperature of the transported fluid is not too low.
Reference can be made in this connection to patent application EP-A-323,774 in the name of the present applicant, which describes the use of nonionic, amphiphilic compounds chosen from among esters of polyols and carboxylic acids, in substituted or unsubstituted form and imide function compounds. Patent application EP-A-323 775 in the name of the present applicant, more particularly describes the use of compounds belonging to the group of diethanol amides of fatty acids or fatty acid derivatives. U.S. Pat. No. 4,856,593 describes the use of surfactants such as organic phosphonates, phosphate esters, phosphonic acids, their salts and esters, ionic polyphosphates and their esters, as well as polyacrylamides and polyacrylates. Patent application EP-A-457,375 describes the use of anionic surfactants, such as alkyl aryl sulphonic acids and their alkali metal salts.